It is (in)famously said of Christian anthropology by the atheist existentialists that "the 'yes' to God is the 'no' to Man." The point of course is that the Christian imperative that Man must subject himself (intellect, will, senses, and appetites) ultimately to the divine such that he becomes an instrument of God's essential love is the most definitive denial of human nature, which generates a perpetual, repressive strife between this obedience and self-affirmation. On the surface, at least to the moderately religious, secular Christian, this reveals the (so perceived) repugnant essence that is Christianity and is why this type of "believer" will go to the most hypocritical, incoherent, extremes to find the most liberal, all-inclusive, permissive, watered down, psychologically reductionist branch of the faith possible. This type of believer buys into the existentialist's gross caricature of the faith, is horrified, and simply abandons authentic Orthodoxy in place of something that can only be rightly called Christian Atheism with non-theological spiritual jargon sprinkled on top, leaving behind a philosophically incoherent monstrosity of classic nonsense. But is this an accurate description of the God↔Man dynamic? I would vehemently argue the absolute contrary which has been the Orthodox position since the inception of Christianity, affirmed by the patristic Fathers of the faith all the way up to the present day.
While it is certainly true that Christian living calls for a radical reformation of one's lifestyle and will require the sacrifice of many sacred cows, Christianity in no way amounts to a denial of human nature. In fact, authentic Christianity calls for an elevation of the human person to that which is most authentically human and therefore most affirming of one's human nature as such. How come? Well, in order to establish this it is necessary to venture into some natural theology and metaphysics. The classical and medieval philosophical Tradition typically understood God not as “ens sumum” (highest being) but “ipsum esse subsistens” (the sheer act of “to be” itself). To be God, therefore, is to be, “to be”. To be me is to be human; to be a tree is to be a tree; to be Fluffy is to be a cat. But to be God is simply to “be”. Therefore, God is not the highest being among us lesser beings. He is not the supreme instance of the genus of “being”. God, rather, is the sheer act of Being, or existence, alone in which we individual beings participate in this existentially basic essence, which in its unconditionality is God. We can see now, at least from a metaphysical perspective, to speak of a competitive relationship between God and man would be to make an egregious category error. It’s to misunderstand who God is and who we are. We are not in competition with the Almighty; we are in a relationship with the Almighty.
As such, we are most ourselves and God is most Himself when we are put in our rightful places. Just as a mother plays her role best when she acts as mother, and a child plays his or her role best when he or she acts as the child. Every relationship works best when both parties fit their roles properly according to their natures. To act in contradiction to this order would generate disorder and in the long run misery. So with God. We find our fulfillment not when we try to become God, or when we grovel like slaves, but when we fulfill our natures in accordance with God’s Divine Idea of the Human essence. Since God is subsistent Being Itself, the Divine Ideas (forms) in their ideal state are perfected according to their natures. Thus when we orient ourselves to Jesus who is the God-Man, we will find our fulfillment, for we will be perfected in accordance with our natures because we have becomes aligned to the true manifestation of Aristotle’s Magnanimous Man, or better, the God-Man, which is God Himself made flesh, the ideal essence of what it means to be authentically Human. We are called to divinization and we ought not settle for second best. We shouldn’t, therefore, fall into this delusion that the “yes” to God is the “no” to Man, for it is precisely to opposite. When we say no to God, we deny ourselves because our essence of what it means to be Human is an Idea spoken from the lips of God Himself. And so if there is anyone we ought to say yes to, it ought to be to God, for it is from God that we have our being, and it is therefore to God that we will find our telos, our last end.
Christianity, therefore, apart from being a life-denying puritanism is the ultimate humanism. It calls for human beings to elevate themselves through cooperation with the Divine grace in order that they might be perfectly aligned with what it truly means to be authentically human, matched up with the Divine Idea of the essence of Humanity, thought first by God and brought to completion through our cooperative love. In closing, “the glory of God is a human being fully alive” (St. Ireneaus).